1. Field of the Invention
Generally, the radial carcass reinforcement of the tire in question, which is formed of inextensible reinforcement elements made of metal or of aromatic polyamide, is surmounted radially by a crown reinforcement comprising a plurality of crown plies; in particular a triangulation ply formed of metallic elements which are oriented relative to the circumferential direction by a large angle of between 45° and 90°, said triangulation ply in turn being surmounted by two working plies formed of inextensible metallic reinforcement elements which are parallel to each other within each ply and are crossed from one ply to the next, forming angles of between 10° and 45° with the circumferential direction. Said working plies, which form the working reinforcement, may also be covered by at least one so-called protective ply, formed of generally metallic, extensible reinforcement elements, which are referred to as elastic elements.
2. Description of the Related Art
Cables are said to be inextensible when said cables have a relative elongation at most equal to 0.2% under a tensile force equal to 10% of the breaking load.
Cables are said to be elastic when said cables have a relative elongation at least equal to 4% under a tensile force equal to the breaking load.
The circumferential direction of the tire, or longitudinal direction, is the direction corresponding to the periphery of the tire and defined by the direction of rolling of the tire.
The transverse or axial direction of the tire is parallel to the axis of rotation of the tire.
The radial direction is a direction intersecting and perpendicular to the axis of rotation of the tire.
The axis of rotation of the tire is the axis around which it rotates in normal use.
A radial or meridian plane is a plane containing the axis of rotation of the tire.
The circumferential median plane, or equatorial plane, is a plane perpendicular to the axis of rotation of the tire and which divides the tire into two halves.
In the case of tires for “heavy vehicles”, a single protective ply is usually present and its protective elements are in most cases oriented in the same direction and at the same angle in absolute value as those of the reinforcement elements of the radially outermost and hence radially adjacent working ply. In the case of construction-vehicle tires which are intended to travel on relatively bumpy roads, the presence of two protective plies is advantageous, the elastic elements being crossed from one ply to the next and the reinforcement elements of the radially inner protective ply being crossed with the inextensible reinforcement elements of the radially outer working ply adjacent to said radially inner protective ply.
Application JP 59/118507, with the aim of avoiding separation between crown plies, shows such a reinforcement structure with a radially outer ply on one hand formed of high-modulus textile reinforcement elements forming with the circumferential direction an angle which in absolute value is smaller than the angle formed by the elements of the radially outer working ply, and on the other hand having an axial width greater than the width of said working ply, while remaining less than the width of the radially inner working ply.
Application JP 03/262704, with the same aim, describes and shows a solution very close to the previous one as far as the axial widths of the plies and angles of the reinforcement elements of said plies are concerned. Furthermore, it specifies that the radially outermost ply has an elongation at break of at least 5%.
With the aim of protecting the working plies from corrosion, and avoiding separation between the crown reinforcement and tread, document JP 04/055 104, which adopts practically the same axial widths of crown plies, advocates using reinforcement elements of aromatic polyester for the protective ply.
French Patent 2 493 236, with the aim, it would seem, of solving the problems posed by travel on a rough road, advocates a structure similar to the previous ones, but with use in the radially inner and outer plies of reinforcement elements, the elongation at break of which is greater by at least 40% than the elongation at break of the reinforcement elements of the two working plies.
The progress made in terms of length of life (number of kilometers traveled) on wear of “heavy-vehicle” tires, and also the possibility of easy, economical subsequent retreading, requires a crown reinforcement, the resistance to separation between the edges of working plies of which is improved.
Patent FR 2 800 672, in order to limit separation at the ends of working plies, claims a crown reinforcement structure in which a ply, referred to as a protective ply, has an axial width between those of the working crown plies, the reinforcement elements of the protective ply being inclined in the same direction as the reinforcement elements of the radially adjacent working ply and forming with the circumferential direction an angle greater, by at least 5°, than that of said radially adjacent working ply.
In their research and in particular during research into the production of “heavy-vehicle” tires having an increasingly long wear life (number of kilometers traveled), the inventors set themselves the task of defining a tire crown structure which makes it possible to obtain a resistance to separation between the edges of working plies which is improved still further.